Joining a ZeroTier network is like connecting the same WiFi or plugging in to the same Ethernet switch as your other devices, so things mostly "Just Work". Many virtual network products do not have this convenient property. ZeroTier works at Layer 2.
Look at the Network section of Finder’s sidebar
It seems to take a while for Macs to notice each other the first time. Then they start showing up in the Network tab of the Finder.
That's pretty much it. Screen Sharing and Media Sharing should work over ZeroTier too.